In-Plane Vibrometer - Features

In-plane vibrometers comprise two functional components, an optical head, (LSV-065-306F), and a controller. Polytec offers two different controllers for its in-plane laser vibrometers. 

LSV-065-306F Optical Head

The LSV-065-306F optical head operates on the differential laser Doppler principle. The beam of a wavelength-stabilized diode laser is split into two smaller beams, which are then converged at a known angle on the surface to be measured.

Overlapping of the beams results in a three-dimensional region (measurement volume), which contains an interference pattern (bright and dark fringes), that are a distance dx apart. The fringespacing dx depends only on the beam intersect angle and the laser wavelength, both of which are known and constant. 

A frequency shift between the two laser beams generated by the Bragg cell causes the fringe pattern to translate through the measuring volume. Light scattered from each point on the measured surface, modulated by the fringe pattern, is collected by a lens and focussed onto a detector. The modulation frequency of the detected light will change proportional to the surface velocity perpendicular to the fringe pattern.

The signal will have a DC component proportional to the average speed and an AC  component corresponding to the variations around that velocity. The frequency shift enables the vibrometer to detect the direction of the surface motion and measure inplane vibration around zero velocity.

OVF-3310 and OFV-3320 Controller

Polytec offers 2 different controllers for its in-plane laser vibrometers:
 

• The OFV-3310 uses analog FM demodulation electronics to analyze the Doppler shift. The Purpose of the OFV-3310 is to measure the variation component (AC) which is on top of a constant speed (DC).The microprocessor integrated in the OFV-3310 calculates and shows the DC velocity on the LCD display.The DC value is accessible via the integrated interfaces as well. The AC signal represents dynamic velocity fluctuations superimposed on the average DC value.The frequency range in question can be selected by finely adjustable filters with a span up to 51 kHz. The analog AC and DC signal are available on 2 BNC sockets on the front panel of the controller

• When high frequency in-plane vibrations have to be measured, model OFV-3320 controller is the choice.